Calibration of photo-detectors is required in many supplications. There are two types of calibration for photo-detectors. The first type is a relative calibration for elements of a photo-detector array that reduces non-uniformity across the elements of the array. The second type, which is the subject of the present disclosure, is an absolute calibration that allows photo-detector to provide an absolute measurement of intensity or radiance. The absolute calibration is also referred to as a radiometric calibration. In particular, the number of photons striking the detector in a given time interval (the integration time) can be determined from the electrical output of the detector using the results of the calibration. Radiometry is a set of techniques for measuring electromagnetic radiation.
Photo-detector arrays, such as charge-couple device (CCD) arrays for example, need to be calibrated to identify bad pixels and achieving non-uniformity correction. This is commonly accomplished using dark frames and compensates for relative differences in the sensors of an array However, since only the relative responses of the detectors in the array are computed, this kind of calibration technique does not achieve absolute or radiometric calibration of the array.
Common procedures for radiometric calibration utilize a calibration source, that is a source with a known radiance. This process can be used to calibrate photo-detectors as long as a calibration source is available and is well characterized.
A previous attempt at creating a procedure for calibrating a photo-detector using the underlying Poisson nature of the photo-detection required calculations of the skewness of the photo-detector measurements. However, the approach relies on estimating the third central moment of measurement. This estimation may require thousands of measurements. This is a lengthy procedure, especially when all elements of an array are to be calibrated.
Accordingly, there exists a need to provide a radiometric calibration procedure that can determine calibration parameters from a reduced number of measurements without the use of a calibrated source of known radiance.